As people's interest in whitening their teeth increases, a number of toothpastes having teeth whitening effect have become commercially available. However, even though the toothpaste contains a teeth whitening agent having good performance, it is hard to achieve significant whitening effect in a short period of time by brushing teeth with only 1 to 3 minutes of contact time between teeth and toothpaste.
Recently, in order to solve the above problems, a number of patent applications related thereto have been filed and teeth whitening products of various formulations have appeared on the market.
For example, in the case of professional whitening gel, a dentist manufactures an individualized mouth tray, which precisely fits the teeth of the patient. The patient applies the whitening gel in a prescribed amount to inner walls and trough of the tray following instructions at home. Therefore, this whitening method has disadvantages in terms of convenience and cost. Furthermore, this method may present problems with safety and comfort, since the surplus peroxide gel and the mouth tray itself may cause irritation or damage to the gums or oral cavity.
In order to solve these problems, Japanese Patent No. 10,017,448, assigned to Lion Corp., discloses a sheet-shaped oral plaster, which comprises a teeth adhesive layer and supporting layer. A whitening agent used in the plaster includes kojic acid and derivatives thereof, ascorbic acid and derivatives thereof, carbamide peroxide and the like, among which kojic acid and various salts thereof are described as being effective. However, the above-mentioned whitening agents have a strong acidity, which may cause irritation to oral cavity. Further, since these agents effect whitening at a high acidity, it is difficult to produce good whitening without irritation. When this two-layer patch structure contains a high reactivity material such as a whitening agent, its stability degrades at high temperatures even though being stored with a release liner attached.
U.S. Pat. Nos. 5,879,691, 5,891,453 and 5,989,569, and WO 98/55044, assigned to Procter & Gamble, disclose a delivery system for a teeth whitener, comprising a thin, transparent and flexible polyethylene strip having a professional whitening gel thereon, wherein the professional whitening gel is pre-coated during the manufacturing process or applied to the strip or teeth directly before the attachment to the teeth. Since it does not use a mouth tray, the usage is facilitated and improved. Further, because the strip is thin and transparent, its use does not present an obstacle to the daily life. However, the delivery system disclosed therein is a wet type whitening layer constructed by using a teeth whitening substance along with a gelling agent, preferably carboxypolymethylene, obtained from B. F. Goodrich Company under the trade name of Carbopol, water, pH adjusting agent and additive carrier materials and applying the resultant highly viscous gel onto a strip of flexible polyethylene strip. When attaching and wearing the system onto teeth, the teeth whitening gel containing high concentration peroxide may adhere to and remain on hands, tongue, gums and the like. That is, such wet type gel systems have room for improvement in terms of handling. Further, in the two-layer embodiment consisting of a teeth whitening substance and strip, the peroxide stability is not sufficiently assured and the whitening effect may be diminished when stored at a high temperature or for a long period of time.
U.S. Pat. Nos. 5,310,563 and 5,639,445, assigned to Colgate-Palmolive Company, disclose a dental formulation comprising an active component dispersed in a polysiloxane polymer composition, available under the trade name of Dow Corning 3179 Dilatant Compound by Dow Corning Corporation, which is attached to the teeth by pressing it against the teeth and gum, and is easily removed from the teeth. The two-layer embodiment has the active whitening component encapsulated in the polymer. Therefore, the stability of the active peroxide component can be improved to some degree. However, this product has a disadvantage in that the active ingredient cannot be easily released from the Dilatant Compound in a short period of time, and consequently, an extended contact time is required to obtain the desired teeth whitening effect.
Therefore, there is a need for a dry type teeth whitening patch, which has improved peroxide stability at high temperature and safety to the human tissue during its attachment to the teeth.